Process for dyeing textile fibers with vat dyes



Nov. 8, 1949 P. H. STOTT r AL 2,487,197

PROCESS FOR DYEING TEXTILE FIBERS WITH VAT DYES Filed March 11, 1944 INVENTORS PHIL/P H; srorr and RICHARD A. SH/MP ATTORNEY Patented Nov. 8, 1949 raocnsjs roa nvnmo 'rnx'rmn mans wrrn var DYES 1 Philip H. Stott, Woodstown, and Richard Shimp, Woodbury, N. J., assignors to E. I. du Pont de Nemours & Company, Wllmin a corporation of Delaware gton, Del.,

Application ,Mmu 1944, Serial No. 526,118 I There are two general methods in practice today for dyeing piece-goods-with vat dyes. The first process, and the only one which has been adapted for the continuous dyeing of piece-goods as distinguished from batchprocesses, is the one in which the vat color is applied to the goods in the reduced form. Such processes are illustrated in the patent to Tice U. S. P. 1,652,649,- and the more recently developed process of Wentz U. S. P. 2,318,133. The dyeing of the fiber from solutions of the reduced color presents some diiflculties, however. In the first place, the amount of dye that can be applied to the fiber will depend upon how soluble the color is in the reduced form, and the aflinity ofthe dye for the fiber. Many of the anthraq'uinone vat colors are not readily soluble in the vat, and thereforeit is difllcult toapply them in'the heavy shades required .in some cases without running them through the dye bath a second orthird time. It has also been found difllcult to dye to an improvement in 2 Claims. (01. 8-1495) cotton goods evenly in very weak or pastel shades that, when dyeing in heavier shades with those vat dyes that are sufllciently soluble to be applied in heavyshades, it is diflicult in many cases to obtain the desired penetration so that the cloth is dyed evenly throughout.

liquid from which the dye must be applied, for even with the more soluble types they have limited solubility even in reduced form.

The second method generally employed in the dyeing of piecergoods is what is commonly referred 'to as the pigment-pad reduction dyeing process, or the pad-jig process. In this-process, the dye in a highly dispersed unreduced) form is applied to the fiber from concentrated suspensions, and this finely suspended dye is forced into the fiber as the cloth .passes between squeeze rolls. The cloth is .then run into rolls either without or after drying. These rolls are then put in a jig in which the goods is run back and forth several times through an alkaline reducing solution until the reduction "and fixation of the dye on the fiber is complete. The- The reduced vat: dyeing processes also require large volumes of;

goods is then run through an oxidizing bath, or

otherwise oxidized, then rinsed, soaped, re-rinsed and dried in the customary manner. This padjig process permits the application of the dye in as heavystrengths as desired, and the amount of water employed can be reduced to only that required to carry the suspended color into the fiber under pressure of the squeeze rolls. This process, however, requires a large amount of handling of the gOOdS and an unnecessary length of time in passing the goods back and forth through the reducing solution on the jig. Furthermore, because the fabric containing the solution of the dye comes in contact with air, there is some surface dyeing which is objectionable.

It is therefore an object of the present invention to provide a process for applying vat dyes to'textile fibers by a. pigment-pad process wherein the goods can be continuously padded and developed without extra handling and without any chance for surface oxidation. A further object of the invention is to provide a continuous piece-goods dyeing process which will give results dilute suspensions of the insoluble vat dyev as more particularly illustrated in the following examples, and then passing the cloth through a reducing solution at a temperature belowthat at which actual reduction of the dye takes place, and then immediately passing the goods into an air-free steam chamber, such as of the Mather-Flatt type, whereby reduction and fixation of the color takes Place quickly at temperatures of 212 F. and above. Because the dyeing is thus effected in one pass of the goods through the apparatus, and because the temperature at which the color is fixed is higher than heretofore employed, the time required to effect the dyeing iskept at a minimum. From the steam chamber, the goodsis subjected to the usual oxidation, rinsing, soaping, rinsing and drying operations, all of which can be carried out in the continuous piece in the same manner as .in thereduced-pad continuous dyeing processes.

In the accompanying which forms a part of this specification, a diagrammatic illustration of our dyeing process is given, showing the path of the textile to be dyed as it passes through the various steps in the process. In the drawing, the numeral I represents the textile which first passes through the padder 2 which contains the dispersed vat dye in pigment form, then through the nip rolls 3 which ordinarily constitute part of the padding apparatus; from there into the drier 4, then the goods'is cooled in any conventional manner such as Passing over the cooling can 5 so that the temperature of the goods as it passes through the caustic and hydrosulfite solution in the padder 6 is below that at which reduction normally takes place. After passing through the nip rolls 1 of the padder, the goods is immediately passed into an air-free steamer 8, then through the oxidizing, soaping and rinsing baths III, II and :2, respectively, and finally passed over the drying rolls I 3.

By passing the goods directly from the reducing solution into an atmosphere of steam from which all oxygen is excluded, no undesirable surface oxidation takes place and the reduction and fixation is effected so rapidly that there is no appieciable migration of the dye to the surface of the goods. By this process, the goods is dyed evenly throughout and maximum fastness of the dye is obtained.

After padding the goods with the. unreduced vat color, it is preferably dried by passing it through a hot flue or over dry cans, for this permits better control in adding the chemical pad, that is, the caustic and reducing agent, and permits the amount of water remaining in the cloth to be held at a minimum. Because reduction is not brought about until the cloth enters the steam, and because the color is fixed at the higher temperatures, migration ofthe color in the goods is kept at a minimum.

If the chemical pad is applied to the wet pigmented goods, the moisture content of the final chemically padded goods should not be over 100% based on the weight of the dry goods. Control of this moisture content of the impregnated fabric prior to steaming has been found desirable in the production 01' level dyeings, for excessive moisture will tend to cause streaking, while insufiicient water will result in poor development and therefore not a complete utilization of all of the color applied to the goods. 4

with most dyes, very satisfactory results are obtained when the moisture content of the goods as it enters the steam chamber is maintained between 50% and 100%, based on the weight of the fabric. with very difilculty vat-soluble colors, a higher moisture content may be desired. A higher moisture content may be employed on some goods than on others with equally good results, depending upon the texture and nature of the fibers being dyed.

The concentration of the caustic and hydrosulfite in the chemical bath maybe varied widely, as long as sufficient is employed so that, for the particular moisture retention allowed, complete reduction and development in the steam chamber is effected. Where the padder is set to retain 50% moisture from the chemical padding operation, a concentration of 4 ounces of caustic and 4 ounces of hydrosulfite per gallon is usually sufilcient.

To prevent premature reduction of the dye on the fiber, the chemical padding operation. wherein the reducing agent and caustic are applied, is preferably carried out at temperatures not over the invention.

4 r. although temperatures unto r. may be used The time of immersion in the chemical Dad should be from 2 to 10 seconds, although a longer time may be required for certain types of fabrics. The time should be kept at the minimum required to obtain complete penetration of the chemical solution throughout the goods.

Following the chemical padding operation, it is desirable that the goods be passed as directly and quickly as possible into the steam chamber to avoid any tendency toward decomposition of the reducing agent, or oxidation of reduced dye. Experience has shown that no appreciable decomposition can be detected when the padding is carried out at temperatures not higher than 90' 1".

and after 10 seconds exposure prior to entering the steam chamber. This permits considerable leeway in leading the goods from'the chemical pad to the steam chamber.

The steaming operation is preferably carried out at temperatures of from 212 to 240' 1''. At these temperatures substantially complete reduction and fixation are obtained in from 15 to 45 seconds. Longer periods of steaming may be employed when necessary. While periods of steaming longer than that actually required to eifect complete reduction and fixation of the color may be employed without detriment to the resulting dye, it merely adds unnecessarily to the cost of the process, and is therefore to be avoided.

After development and fixation of the color in the steamer, the cloth is run into the usual oxidizing baths. Chromic acid, sodium perborate, hydrogen peroxide, or other oxidizing agent may be employed, or the material may be oxidized with air. After oxidation, the goods is soaped, rinsed and dried in the usual manner.

To facilitate the chemical padding operation, wetting agents may be employed. Alkanol B (sodium alkyl-naphthalene sulfonate) operates very eflectively for this P pose when added to the reducing bath.

The following examplesare given to illustrate Unless otherwise parts used are by weight.

Example 1 Cloth is run through a padder set to' retain 50% moisture containing the following pigment dyestufl suspension:

Ponsol Jade Green Paste (11.6 color solids) (C. I. 1101).... --ol. I Water gal-.. 1 Alkanol B (sodium alkyl-naphthalene sulfonate on-.. 0.15

Caustic soda fl. 4 Sodium hydrosulfite oa 4 Sodium chloride ..os 4 Water gaL- 1 Temperature: 90' 1''. Time of immersion: 5 seconds.

impregnated fabric a then passed uirourn "a substantially oxygen-free steam chamber (212-215 1".) for a duration of 45 seconds. The dyestulf is in reduced form upon leaving the 75 steamer, and is subsequently oxidised in the conp cified, the

ventio'nal manner in 0.25% sodium bichroma'rc solution containing 0.50% acetic acid. It is then rinsed in cold water, soaped, rinsed and dried.

Comparative dyeings were also made by developing the pigment vat color impregnated fabric on a ji'gger in the conventional manner.

Dyeings made bythe newsteam process ,were

equal in pex'uetration, shade'andbrilliancy, but showed superiorfastnessto laundering and scrubbing when compared with those products on the jigger in the conventional manner.

is made to 1 liter. with water. This mixture is padded on herringbone twill fabric at 140 F., with the padder set for 50% moisture retention and the impregnated'goods then dried.

The impregnated fabric is then padded with 50% moisture retention with a solution consisting of: i

g Ounces per. gallon Caustic soda- 1.5 Sodium hydrosnlfite At room temperature (70 F.).

The fabric is then passed into a substantially oxygen-free steam chamber for. 1 minute, oxi-' dized in the conventional manner in 0.25%

chrome acetic acid solution, rinsed, soaped,'rinsed and dried. y l A comparative dyeing was made by developing the pigment impregnated fabric in a jigger containing 1.5" oz. per gallon 'caustic'soda and 4 oz. pergallon sodium'hydrosulfite at 140 F.'for onehalf hour, oxidizing and finishing as usual.

Olive-drab shades were obtained in both instances, and the dyeing obtained with steam process was fully equal in strength, shade and brilliancy versus the conventional ii ger developed dyeing.

Example 3 Ponsol Blue GD paste (C. I. 1113) (color solids 16.4) oz..- Water gal 1 Temperature: 140 F.

The pigmented goods is dried in a hot flue and padded with 50% moisture retention in a chemical solution containing:

Ounces Caustic soda 1.5 Sodium hydrosulfite 1.5

Sodium chloride 2 Temperature: 90 F. Time of immersion: 5 seconds.

The impregnated goods is then passed directly through an air-free steamer (212 F. to 215 F.) for a duration of seconds. The dyestufi is in reduced form upon leaving the steamer, and is subsequently oxidized, rinsed, soaped, rinsed and .dried.

Example 4 j By this rocess Indian Head fabric. which'is a highly mercerized and tightly woven fabric ordinarily very difficult to penetrate withdyes. can be dyed rapidly and very. satisfactorily-asfollows:

The cloth is run through a padder, set to re tain 50% moisture, containing the following pigment dyestufl suspension which is held at 140 F.:

' Ounces per gallon The dyestufl of Example 1 of us. P. 995,-

936 0.147 The dyestuif of Color Index #1101 f0.116 The dyestuff, of Example 5 of U. S. P.

1,705,023 0.0597 Alkanol 13 (sodium alkyl naphthalene sulfonate) L .0400

This padded fabric dried in a hot flue and padded with the following chemical pad, the

squeeze rolls being set so that the goods will retain 50% moisture.

Caustic soda; -oz 2 Sodium hydrosulflte oz 2 Sodium chloride oz 2 Water l 1 Temperature: 90 F. Time of immersion: 5 sec onds. Y

The impregnated fabric is then passed through a substantially oxygensfree steam chamber (212-215 F.) for a duration of 45 seconds. The dyestufi is in reduced form upon leaving the steamer, and is subsequently oxidized in the conventional manner in' 0.25% sodium bichromate solution containing 0.50% acetic acid. It is then rinsed in cool water, soaped, rinsed and dried.-

The dyeings made by thisprocess are of good strength, shade and brilliancy, ,but show excellent fastness to laundering and scrubbing and the process of Example 1 or Example 3.

The process of this invention is applicable for the dyeing of warps, skeins or any other form of textile fiber which can be introduced into the pigment pad, chemical pad and development chamber in a continuous manner. It is of course understood that other vat dyes than those specifically employed in the above examples may be dyed by this method, such as the thioindigos. sulfur colors, and any others which may be dyed by the vat dye method.

In place of the sodium hydrosulflte, other reducing agents which operate in a similar manner may be employed. With milder reducing agents, a longer time of development in the steam chamber is required, as is also the case with certain more diflicultly reducible vat colors. The time required for complete reduction and development in the steam chamber will depend her. is preferably heated quickly to the temperature of the chamber, and the heating should be carried out in such a manner that it is uniiorm on both sides of the fabric, and the steam should fiow through the chamber in such a manner as to remove the decomposition products of the reducing agents at a satisfactory rate. Formation or deposition of moisture, as condensed on the fabric, should be avoided. U

The process as above described provides a very satisfactory method for dyeing goods in a continuous piece and for obtaining dyeings of good penetration and which have maximum fasthess properties, particularly with regard to abrasion and laundry tests. The process permits a material saving in the volume 01 dyeing liquid required, and, since no developing solution is employed, there is no loss of dye in the finally discarded developing bath, for substantially all of the dye which is applied to the fiber is fixed therein. The process permits the dyeing of textile fibers in very even pastel shades, and also permits the application of even the most diilicultly reducible vat dyes in heavy shades.

We claim:

1. A rapid continuous process for dyeing textile fibers with vat dyes which comprises padding the fiber with a dilute aqueous suspension of an unreduced vat dye which'does not contain a thickening agent, padding the fiber containing dye with an alkaline solution of sodium hydrosulfite for a period of from 2 to 10 seconds and at a temperature below that at which any material reduction of the dye takes place, the concentration of the alkaline solution of the sodium hydrosulfite being such that at normal vatting temperatures it will eii'ect reduction of all oi the dye in the fiber, and immediately sub- Jecting the fiber so padded to the action of steam in the absence of oxygen for a period of from to 45 seconds to effect reduction and fixation of the dye in the fiber.

2. A rapid continuous process for dyeing tex- I 8 tile fibers with vat dyes, which comprises paddin the fiber with a dilute aqueous suspension of an unreduced vat dye which does not contain a thickening'agent, drying the sheiso pad ded, padding the fabric containing the dye for a period of from 2m 10 seconds with from to 100%, based on the weight of the fabric, of a caustic alkali solution of sodium hydroaulfite containing from 1.5 to 4 ounces oi each of the caustic and hydrosulfite per gallon of solution maintained at temperatures not over l"., and, as fast as padded, immediately subjecting the fiber padded with the color, caustic alkali and hydrosulfite to the action oi steam in the absence of oxygen tor a period oi'i'rom 15 to 45 seconds to efifect reduction and fixation oi the dyeinthe fiber.

PHILIP H. B'I'O I'I. RICHARD A. 88110..

REFERENCES CITED The ioliowingreierencea are oi recordintho file of this patent:

UNITED STATES PA'IINTB OTHER REFERENCES The Principles and Practice oiTextile Printing," 3rd ed., Knecht and Fothergill (1938) pages 394 to 39s. (Copy in Division 43.) 

